In the use of automatic welding apparatus, such as the apparatus disclosed in U.S. Pat. No. 4,014,495 to Oda et al. and in U.S. Pat. No. 4,229,641 to Ahara, the apparatus is moved automatically through a three dimensional space so that welding operations can be performed at various locations in the three dimensional space. Both of these patents also disclose that the welding tip may be rotated automatically about an axis while maintaining the welding tip on the axis of rotation so as to vary the lead or drag angle. However, neither of these patents disclose any means for automatically varying the weld angle of the welding torch relative to the tool. Therefore, with respect to the apparatus disclosed in both Oda et al. and Ahara, when a change in the weld angle is desired, the machine must be programmed to stop while the linkage, illustrated in FIG. 2 of Oda et al and FIGS. 7 and 8 of Ahara, is adjusted to change the weld angle.
A significant commercial market exists for an automatic welding apparatus used in non-repetitive or low volume, repetitive welding applications. Such areas include welding done in fabrication shops, manufacture of machinery structures, farm equipment, off highway equipment, equipment for the lumber and paper industry, tanks and vessels for the petroleum and chemical industries, and many on-site construction projects, such as shipbuilding. In order to use an automatic welding process in such operations, the teaching time associated with programming the apparatus to follow a desired path must be only a fraction of the weld time, e.g., the operator should be able to program in 1/6 of the actual welding time. Also, the method for programming must be relatively inexpensive since the volume of business is not great enough to afford the expense associated with the present commercialized robotic welding machines.